1. Field of the Invention
The present invention is in the field of devices for dispensing medicaments in powder form without the use of propellants, which are breath actuated, with the medicament dose being inhaled by mouth.
The site of administration of the powder medicament, delivered by devices of the type to which that of the present invention belongs, is the bronchial tubes and their ramifications in the lungs of the patient being treated. Thus, the bronchi and bronchioles are the primary sites of administration. Typically, such a patient may be suffering from asthma or acute or chronic bronchitis, and it is essential that the powder dose of medicament reach and be applied uniformly to as much of the surface of the bronchi and other parts of the lung as possible.
In order to achieve this objective, the powder medicament is usually in the form of extremely fine particles, preferably in the size range of from 1 to 10 microns. In order to achieve the necessary particle size distribution for the powder medicament to be used in a powder inhaler device, techniques such as controlled crystallization will be employed. One may also use anti-agglomerating agents to ensure that there is no clumping together of the extremely fine particles, which have a natural tendency to flocculate together due to the static charge which such fine particles normally acquire.
The powder medicament for use in the powder inhaler device of the present invention may also be hygroscopic in nature, causing particle aggregation while the dose is still resident in the powder inhaler device, and also causing particle growth during inhalation. Problems of hygroscopicity may be overcome by a portective coating on the medicament particles, or by use of a dessicating excipient.
Thus, the powder medicament for use in the powder inhaler device of the present invention must be fine, i.e., 1-10.mu., and substantially free from any tendency to agglomerate.
The powder inhaler devices of the type to which that of the present invention belongs do not require the use of propellants, and thus represent an advance in the art over those devices which dispense metered doses of a powder medicament with the assistance of a propellant gas. Predominantly, the propellant of choice is FREON.RTM., one of various nonflammable fluorocarbons. However, use of this particular propellant has been the object of recently passed environmental laws which severely restrict its use or even ban it outright. Furthermore, fluorocarbons may actually aggravate the condition of patients suffering from asthma and acute or chronic bronchitis, thus creating a further reason to avoid this nearly universal propellant. While attempts have been made to substitute other propellant gases for the fluorocarbons, these attempts have experienced problems and have not met with uniform success. Thus, there remains a need for efficient powder inhaler devices which are breath actuated.
The powder medicaments which are dispensed by powder inhaler devices of the type to which that of the present invention belongs are typically very potent and are thus delivered in relatively small doses. Consequently, it is also very important that the doses of powder medicament which are delivered be very uniform in amount, i.e., volume. Even though the total amount to be delivered may be augmented by the use of carriers and other excipients well known to the pharmaceutical formulator, it is still critical that there be a high degree of uniformity in the doses delivered.
In addition to all of the above, it is further necessary that a powder inhaler device be simple and economical to manufacture, capable of isolating the powder medicament dose in a tamper-proof and moisture-proof environment, and reliable in repeated use.
Efforts have been made in the past to create powder inhaler devices which do not rely on propellants, but which still satisfy all of the other requirements for such devices and overcome the problems outlined above. These efforts have met with varying degrees of success, as the following discussion of prior art devices makes clear.
2. Brief Description of the Prior Art
Powder inhaler devices have been used in the past which dispense unit doses of medication from prefilled capsules. However, in order for such devices to function properly, the capsule must be correctly positioned in the device which, when actuated, either punctures or pulls the capsules open. Such devices are prone to incorrect dosing, particularly by children, the elderly, and patients with impaired motor function. Moreover, pieces of the gelatin capsule shell may be dispensed with the medication.
Other devices utilize a disc with multiple cavities, each containing a unit dose of medicament covered by aluminum foil. The medication is dispensed by puncturing the aluminum foil covering the cavity. However, such devices have the disadvantage of a potential risk that small pieces of the aluminum foil might be inhaled.